CN113591358B - Dynamic adjustment method for pouring temperature and allowable maximum temperature of mass concrete - Google Patents
Dynamic adjustment method for pouring temperature and allowable maximum temperature of mass concrete Download PDFInfo
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Abstract
The invention provides a method for dynamically adjusting the recommended pouring temperature and the allowable highest temperature of a large-volume concrete. According to the method, the recommended pouring temperature and the allowable highest temperature of the mass concrete are determined on the basis of finite element calculation and analysis, and not only the height of a controlled area from a building base surface, but also the tensile stress of the interior of the concrete in the area are considered. The invention can save construction cost to the maximum extent while guaranteeing construction safety.
Description
Technical Field
The invention relates to a method for dynamically adjusting a recommended pouring temperature and an allowable highest temperature in a large-volume concrete pouring process, and belongs to the technical field of hydraulic and hydroelectric engineering.
Background
Currently, in many hydraulic structural design specifications, regulations concerning the temperature control of bulk concrete only define the allowable temperature difference of the concrete in the foundation constraint areas (i.e. the strong constraint area and the weak constraint area), i.e. the difference Δt between the highest temperature and the lowest temperature allowed for the concrete casting within a height range from the foundation surface h. The concrete gravity dam design specification SL319-2005 specifies the foundation temperature differential, i.e. the maximum temperature allowed by the concrete in the foundation constraint zone and the position within a height range of 0.4L (L is the dimension of the long side of the casting block) from the foundation surfaceStabilization temperatureAnd (3) a difference. When engineering design is carried out, a designer usually carries out design according to design specifications, so that the basic temperature difference inside the concrete is smaller than the allowable temperature difference, and the allowable temperature differences of the mass concrete with different heights and different lengths are given by the design specifications of the table 1.
TABLE 1 Foundation constraint zone concrete allowable temperature differential DeltaT (. Degree.C)
However, it is generally recognized by those skilled in the art that the proposed casting temperature and maximum allowable temperature of the mass concrete cannot be determined only according to the design specifications, that only the height h of the base constraint zone from the base surface should be considered, and that the stress of the constraint zone should be considered. Because the purpose of controlling the temperature of the mass concrete is to prevent the concrete from generating temperature cracks, the reason for the concrete to generate temperature cracks is that the tensile stress generated in the concrete is larger than the tensile strength of the concrete, so that cracks are generated.
Moreover, the finite element calculation result shows that when the width of the bottom of the dam body is larger, the temperature and stress in the constraint area are larger, and the allowable temperature difference away from the concrete on the foundation surface can be further widened. For example, a large ancient hydropower station located in the Sangusi county in the southward area of the Tibetan autonomous region is a second-level hydropower station from the Sangusi county to the Canada county canyon section of the Yaruu Tibetan Jiang Zhongyou, the upstream distance of the second-level hydropower station is about 8km from the Bayu hydropower station planned and developed, and the downstream distance of the second-level hydropower station is about 7km and 18km from the street hydropower station planned and developed, respectively. Taking the temperature control calculation result of the hydropower station as an example, the highest temperature and the maximum stress in Cheng Hunning soil of different heights of the hydropower station and a building base surface are shown in table 2. The stable temperature near the foundation surface of the ancient hydropower station is about 9 ℃, the highest concrete temperature at the position 10m away from the foundation surface is slightly higher than the highest concrete temperature at the position 3m away from the foundation surface, but the concrete stress at the position 10m away from the foundation surface is obviously lower than the concrete at the position 3m away from the foundation surface. It follows that for a large volume concrete project the maximum temperature allowed inside the concrete is related to the stress inside the concrete ≡!
TABLE 2 different altitude temperatures and peak along river stress
| Height/m | 1.0 | 2.0 | 3.0 | 5.0 | 10.0 | 15.0 | 25.0 | 35.0 | 45.0 |
| Maximum temperature/. Degree.C | 24.32 | 21.11 | 20.55 | 21.39 | 21.17 | 20.49 | 17.11 | 17.5 | 22.09 |
| Maximum stress/MPa | 1.02 | 0.92 | 0.93 | 0.91 | 0.75 | 0.55 | 0.12 | -0.02 | 0.20 |
The internal temperature change process of the mass concrete is that the temperature is firstly increased and then is decreased. The temperature rise stage forms compressive stress, and the temperature reduction stage forms tensile stress; the compressive stress in the temperature rise stage is generally smaller than the tensile stress formed in the temperature drop stage, so that the interior of the mass concrete tends to show tensile stress when the mass concrete reaches a stable temperature. Current design specifications only specify the allowable temperature difference and do not establish the relationship of casting temperature and maximum temperature. When the highest temperature is consistent with the concrete stabilization temperature, the stress when the concrete reaches the stabilization temperature is closely related to the concrete pouring temperature, when the highest temperature is fixed, the lower the concrete pouring temperature is, the larger the compressive stress formed in the temperature rising stage is, and the smaller the tensile stress when the concrete reaches the stabilization temperature is.
Therefore, in the mass concrete engineering, when designing the concrete casting temperature and the allowable maximum temperature, not only the allowable temperature difference but also the relation between the casting temperature and the maximum temperature, namely the change process of the internal stress of the mass concrete, are required to be considered.
Disclosure of Invention
In view of the shortages of the current design specifications, the invention aims to provide a method for dynamically adjusting the pouring temperature and the allowable maximum temperature of large-volume concrete. When the method is used for determining the pouring temperature and the allowable maximum temperature of the large-volume concrete, the distance relation between the maximum temperatures of different heights and the building base surface is established by considering the heights of the building base surfaces of different heights Cheng Juli, and the tensile stress in the elevation concrete, namely the relation between the pouring temperature of the elevation and the allowable maximum temperature, is also considered.
In order to achieve the above purpose, the present invention adopts the following technical scheme: a method for dynamically adjusting the pouring temperature and the allowable maximum temperature of mass concrete comprises the following steps:
A. setting the casting temperature of the stress maximum point of the constraint zone as the lowest casting temperature T pc1 The allowable maximum temperature T is defined by the specification of a strong constraint area mc1 Establishing a finite element model to calculate the corresponding stress as the maximum stress f (h 1 )；
B. The pouring temperature is increased, and the distance building base plane h is found according to the finite element model analysis and calculation k Such that it:
f(h k )＝f(h 1 ) (1)
C. obtaining a distance building base surface h according to the relation diagram of the pouring temperature increment, the temperature peak increment and the distance between the pouring temperature increment and the building base surface obtained in the step (1) k Casting temperature T at standard state of point (C) pck And is far from the building base surface h k Maximum allowable temperature T in standard state of point(s) mck ：
T pck ＝T pc1 +ΔT pk (2)
Wherein: delta T pk The pouring temperature increment is adopted;
T mnck ＝T mc1 +ΔT mk (3)
wherein: delta T mk Is the temperature peak increment.
D. And (3) according to formulas (2) and (3), the allowable pouring temperature and the allowable highest temperature of each elevation can be obtained.
The invention determines the recommended pouring temperature and the allowable highest temperature of the mass concrete on the basis of finite element calculation and analysis, and considers not only the height of the controlled area from the foundation surface, but also the tensile stress in the concrete in the area. The invention can save construction cost to the maximum extent while guaranteeing construction safety.
Drawings
FIG. 1 is a flow chart of a method for dynamically adjusting the pouring temperature and the allowable maximum temperature of a mass concrete according to the invention;
FIG. 2 is a graph of height versus casting temperature increase for an embodiment of the present invention;
FIG. 3 is a plot of the height versus maximum temperature increase for an embodiment of the invention.
Detailed Description
The structure and features of the present invention will be described in detail below with reference to the accompanying drawings and examples. It should be noted that various modifications can be made to the embodiments disclosed herein, and thus, the embodiments disclosed in the specification should not be taken as limiting the invention, but merely as exemplifications of embodiments, which are intended to make the features of the invention apparent.
As shown in fig. 1, the method for dynamically adjusting the pouring temperature and the allowable maximum temperature of the mass concrete disclosed by the invention comprises the following steps:
A. setting the casting temperature of the stress maximum point of the constraint zone as the lowest casting temperature T pc1 The allowable maximum temperature T is defined by the specification of a strong constraint area mc1 Establishing a finite element model to calculate the corresponding stress as the maximum stress f (h 1 )；
B. The pouring temperature is increased, and the distance building base plane h is found according to the finite element model analysis and calculation k Such that it:
f(h k )＝f(h 1 ) (1)
C. obtained according to formula (1)A relation diagram among pouring temperature increment, temperature peak increment and distance between the pouring temperature increment and the building base surface is obtained, and a distance building base surface h is obtained k Casting temperature T at standard state of point (C) pck And is far from the building base surface h k Maximum allowable temperature T in standard state of point(s) mck ：
T pck ＝T pc1 +ΔT pk (2)
Wherein: delta T pk The pouring temperature increment is adopted;
T mck ＝T mc1 +ΔT mk (3)
wherein: delta T mk Is the temperature peak increment.
D. And (3) obtaining the allowable pouring temperature and the allowable highest temperature of each elevation according to the formulas (2) and (3).
Under different pouring temperatures, the stress is controlled to be f (h) by adjusting temperature control measures (such as water cooling, running water maintenance and surface heat preservation measures 1 ). Obtaining a distance building base surface h in a list form k The point casting temperature and the highest temperature.
The following illustrates the relationship between the casting temperature increment, the temperature peak increment and the distance from the base surface if a map is established. It is assumed that the base temperature is 13℃and the outside temperature is 8 ℃. Feature point h k 1.65m from the base surface.
Radiating heat on the upstream surface and the downstream surface of the model, radiating heat on the ground, and insulating heat on the other surfaces, wherein the surface heat release coefficient is 250 kJ/m2.d DEG C; and (3) carrying out primary and secondary water supply, wherein the water supply temperature is 10 ℃, the target temperature is 8 ℃, the primary water supply time is 0-20d, and the secondary water supply time is 80-170d. Considering the concrete adiabatic temperature rise according to 28 ℃, the half-maturing age is 4d; the elastic model was 30gpa, a=0.4, b=1.0. And (3) calculating concrete stress caused by the heat insulation temperature rise under the condition that the water cooling measures are certain and the pouring temperature is 13-21 ℃. The relationship between the height and the casting temperature increment and the relationship between the height and the highest temperature increment obtained by the calculation conditions are shown in fig. 2 and 3.
Finally, it should be noted that: the embodiments described above are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced with equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (1)
1. A method for dynamically adjusting the pouring temperature and the allowable maximum temperature of mass concrete is characterized by comprising the following steps: it comprises the following contents:
A. setting the casting temperature of the stress maximum point of the constraint zone as the lowest casting temperature T pc1 The allowable maximum temperature T is defined by the specification of a strong constraint area mc1 Establishing a finite element model to calculate the corresponding stress as the maximum stress f (h 1 )；
B. The pouring temperature is increased, and the distance building base plane h is found according to the finite element model analysis and calculation k Such that it:
f(h k )＝f(h 1 ) (1)
C. obtaining a distance building base surface h according to the relation diagram of the pouring temperature increment, the temperature peak increment and the distance between the pouring temperature increment and the building base surface obtained in the step (1) k Casting temperature T at standard state of point (C) pck And is far from the building base surface h k Maximum allowable temperature T in standard state of point(s) mck ：
T pck ＝T pc1 +ΔT pk (2)
Wherein: delta T pk The pouring temperature increment is adopted;
T mck ＝T mc1 +ΔT mk (3)
wherein: delta T mk Is the temperature peak increment;
D. and (3) according to formulas (2) and (3), the allowable pouring temperature and the allowable highest temperature of each elevation can be obtained.
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| CN104790407A (en) * | 2015-04-21 | 2015-07-22 | 长沙理工大学 | Method for adjusting soil pressure influence |
| CN106844990A (en) * | 2016-12-15 | 2017-06-13 | 中国水利水电科学研究院 | Volume of concrete foundation thermal (temperature difference) stress and levels thermal (temperature difference) stress evaluation method |
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| CN102011492A (en) * | 2010-11-25 | 2011-04-13 | 中铁六局集团有限公司 | Method for controlling occurrence of cracks on mass concrete structure |
| CN104790407A (en) * | 2015-04-21 | 2015-07-22 | 长沙理工大学 | Method for adjusting soil pressure influence |
| CN106844990A (en) * | 2016-12-15 | 2017-06-13 | 中国水利水电科学研究院 | Volume of concrete foundation thermal (temperature difference) stress and levels thermal (temperature difference) stress evaluation method |
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